【Unity】解决InvalidOperationException: Collection was modified； enumeration operation may not execute.

        Today I encountered InvalidOperationException when Unity was running: Collection was modified; enumeration operation may not execute.

        After opening the code, I found that the Dictionary data structure was used, but it was not modified in the foreach loop, it was just called in Update.

foreach (var item in statusTimers)
{
	var status = item.Key;
	statusTimers[status] -= deltaTime;
	if (statusTimers[status] <= 0f)
	{
		if (statusesToRemove == null)
		{
			statusesToRemove = new Dictionary<CharacterStatusType, float>();
		}
		statusesToRemove.Add(status, statusTimers[status]);
	}
}

        After carefully checking multiple files, I called an add method in a Ctrip. This method added to the Dictionary. At this time, Update on the other side was in the middle of a foreach traversal, so a conflict occurred and an error occurred.

private IEnumerator CastRoutine()
{
	// ...
	target._stateManager.AddStatus(_addStatus, _statusTime);
}

public void AddStatus(CharacterStatusType status, float duration)
{
	if (!statusTimers.ContainsKey(status))
	{
		statusTimers.Add(status, duration);
		UpdateCurrentStatus();
	}
	else
	{
		// 如果已存在该异常状态，保留较长的持续时间
		float existingDuration = statusTimers[status];
		statusTimers[status] = Mathf.Max(existingDuration, duration);
		UpdateCurrentStatus();
	}
}

        Solution: Unity provides a thread-safe collection class ConcurrentDictionary, which can correctly handle concurrent access to the dictionary in Ctrip. Just replace Dictionary.